Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $48.25   13.265%   $54.6504   $54.65   $54.65   $54.70  
  Purchase #2 $230.29   3.413%   $238.1498   $238.15   $238.15   $238.10  
  Purchase #3 $17.75   9.628%   $19.459   $19.46   $19.45   $19.50  
  Purchase #4 $174.52   12.173%   $195.7643   $195.76   $195.75   $195.80  
  Purchase #5 $80.44   9.594%   $88.1574   $88.16   $88.15   $88.20  
  Purchase #6 $110.87   3.588%   $114.848   $114.85   $114.85   $114.80  
  Purchase #7 $119.72   4.534%   $125.1481   $125.15   $125.15   $125.10  
  7 purchase totals = $781.84       $836.1770   $836.18   $836.15   $836.20